The use of coiled tubing (CT) technology in oil and gas drilling and servicing has become more and more common in the last few years. In CT technology, a continuous pipe wound on a spool is straightened and pushed down a well using a CT injector. CT technology can be used for both drilling and servicing operations.
The advantages offered by the use of CT technology, including economy of time and cost, are well known. As compared with jointed-pipe technology wherein typically 30–45 foot straight sections of pipe are threadedly connected one section at a time, CT technology allows the continuous deployment of pipe, significantly reducing the frequency with which pipe insertion into the well must be suspended to allow additional sections of pipe to be connected. This results in less connection time, and as a result, an efficiency of both cost and time. CT technology also allows fluid to be continuously circulated downhole while inserting the tubular in the well, thereby significantly reducing the likelihood of a stuck tubular.
The adoption of CT technology has been less widespread than originally anticipated as a result of certain problems inherent in using CT. For example, because CT tends to be less robust than threaded pipe, it is often necessary to drill a surface hole using threaded pipe, cement casing into the surface hole, and then switch over to CT drilling. Additionally, when difficult rock formations are encountered downhole, it may be desirable to switch from CT drilling to threaded pipe drilling until drilling through the difficult formation is complete, and then switch back to CT drilling to continue efficiently drilling the well. Similarly, when it is necessary to perform drill stem testing or coring operations to assess conditions downhole, it may again be desirable to switch from CT to threaded pipe and then back again. A switch back to threaded pipe operations may also be desirable to run casing into the drilled well. When conducting CT drilling operations, it is frequently desirable to switch back and forth between a CT drilling rig and a threaded pipe conventional drilling rig, a process which results in significant costs for two rigs and down time as one rig is moved out of the way, and another rig put in place.
A disadvantage of CT drilling is the time-consuming process of assembling a bottom-hole-assembly (BHA)—the components at the end of the CT for drilling, testing, well servicing, etc., and connecting the BHA to the end of the CT. Presently, this operation is commonly performed manually through the use of rotary tables and make-up/breakout equipment. In some instances, top drives are used, but one of the CT injector or the top drive must be moved out, i.e., they cannot both be in line with the borehole. Not only does this process result in costly downtime, but it can also present safety hazards to the workers as they manipulate heavy components manually.
U.S. Publication 2004/0206551 discloses a rig adapted to perform earth borehole operations using both CT and/or threaded pipe, the CT injector and a top drive being mounted on the same mast. The CT injector is selectively moveable with respect to the mast between a first position wherein the CT injector is in line with the mast of the rig and hence the earth borehole and a second position wherein the CT injector is out of line with the mast to allow threaded pipe operations using the top drive.
The disadvantages of the prior art are overcome by the present invention, and an improved rig and method for selectively inserting either coiled tubing or a threaded tubular into a well utilizing a coiled tubing injector or a top drive, respectively, is hereinafter disclosed.